Condensed concepts

How do complex structures emerge from simple systems? How do you define emergence? Conway's Game of life is a popular and widely studied version of cellular automata. It is based on four simple rules for the evolution of a two-dimensional grid of squares that can either be dead or alive. What is amazing is that distinct patterns: still lifes, oscillators, and spaceships can emerge. Gosper's glider gun  is shown below. What does this have to do with strongly correlated electron systems? The similarity is that one starts with extremely simple "rules" : a crystal structure plus Coloumb's law and the Schrodinger equation (Laughlin and Pines' Theory of Everything) and complex structures emerge: quasi-particles, broken symmetry states, topological order, non-Fermi liquids, ... Recently, Sophia Kivelson and Steven Kivelson [daughter and father] proposed the following definition: An emergent behavior of a physical system is a qualitative property that

Although this blog has a wide readership one thing it struggles with is to attract many comments, and particularly much back and forth discussion. Sometimes people tell me that this is just because it is not provocative or controversial enough. A while ago I changed the settings to allow anonymous comments and this has led to an increase in comments which is encouraging. However, I do have some ambivalence about this.  Ideally, any comment and opinion should be judged on the merits of its content not based on who is giving it. We should beware of arguments from authority. On the other hand, that is not the way most of us think and act. We do give some weight to the author. For example, an anonymous commenter says "I am a physicist and I am a climate change skeptic" it does not have the same weight as the opinion of a respected physicist who has relevant expertise. I am also concerned that people are not willing to take the risk of being publically identified with t

Australia has many unique things besides kangaroos and koalas. Long service leave  (LSL) is a generous and egalitarian feature of the "welfare" state. After ten years working for the same employer [or the same sector such as government universities] an employee is granted three months fully paid vacation. (The exact terms and conditions vary slightly between states and employers). LSL is available to all full-time employees, regardless of whether they are janitor or CEO. This is in addition to four (plus) weeks of annual leave and for faculty in addition to "sabbaticals" [called Special Studies Program in my university]. If an employee resigns any unused balance is "cashed out". University faculty work hard and some are workaholics. Many don't even take their allotted annual vacation, let alone LSL. Balances carry over each year and so some faculty have large balances. The "accountants" (who basically run the university) don't like t

I never thought I would write a blog post with such a word in it. In today’s Seattle Times there is an editorial about fake news and an opinion piece, How to fine-tune your BS meter, by Jevin West . At the University of Washington, West and Carl Bergstrom, have started a course entitled, Calling BS: Data reasoning for the digital age. West states: Our philosophy is that you don’t need a Ph.D. in statistics or computer science to call BS on the vast majority of data bullshit. If you think clearly about what might be wrong with the data someone is using and what might be wrong about the interpretation of their results, you’ll catch a huge fraction of the bullshit without ever going into the mathematical details.    Unfortunately, this applies to science as much as to Fake News. On his blog, Peter Woit discusses the rise of Fake Physics. Science is in trouble when the word I most often hear associated with the name of a particular Ivy League science Professor is BS. Furthermore

As part of a TV documentary, Why are we here ? produced by Ard Louis and David Malone there is a nice series of interviews where emergence is discussed by George Ellis , Peter Atkins , and Denis Noble. I can't seem to embed the interviews here and so have put in links to short clips. George Ellis discusses the difference between weak and strong emergence and his attitude to each. In separate clips, Denis Noble discusses emergence  and reductionism in biology. Peter Atkins, a hardcore reductionist, IMHO does not seem to seriously engage with the issue.